1. Field of the Invention
The present invention relates to a colored composition for color filters for use in production of color filters used in, for example, color liquid crystal displays, color camera tubes, and the like, and a color filter formed by using the same.
2. Description of the Related Art
Color filters are made of a transparent substrate such as a glass substrate and filter segments in two or more different colors in the shape of very narrow band (stripe) arranged in parallel or at an angle or minute filter segments arranged orderly in certain vertical and horizontal directions formed on the surface of the substrate. The filter segments have a very narrow width of several microns to several hundred microns and are arranged orderly in a particular pattern respectively according to the colors.
Generally, a transparent electrode for driving liquid crystal is formed on the color filters used in color liquid crystal displays by vapor deposition or sputtering, and an orientation film for orientating the liquid crystal in a certain direction is formed further on the electrode. For obtaining the transparent electrode and orientation film sufficiently high in performance, they should be processed normally at a high temperature of 200° C. or more, preferably 230° C. or more.
Accordingly, the color filters are currently produced mainly by a so-called pigment dispersion method wherein a pigment superior in light stability and heat resistance is used as a colorant, mostly according to the following two methods.
In the first method, a color filter is produced in the steps of coating a pigment dispersion containing a pigment dispersed in a photosensitive transparent resin solution on a transparent substrate such as a glass substrate, drying the coated substrate for removal of the solvent, subjecting the substrate to a pattern exposure for a filter color, forming a pattern for the first color by removing an unexposed portion in a developing process, treating the resulting substrate by, for example, heating as needed, and repeating the similar operations for all filter colors one by one.
In the second method, a color filter is produced in the steps of coating a pigment dispersion containing a pigment dispersed in a photosensitive transparent resin solution on a transparent substrate such as a glass substrate, drying the coated substrate for removal of the solvent, coating a resist such as a positive-type resist on the coated film, subjecting the substrate to a pattern exposure for a filter color, forming a resist pattern by development, removing the pigment dispersion coated film to which no resist pattern is attached with an etchant by using the pattern as an etching resist, forming a patter for the first color by removing the resist film, treating the resulting substrate by, for example, heating as needed, and repeating the similar operations for all filter colors one by one. Development of the resist and etching of the pigment dispersion coated film may be carried out at the same time.
In production of the color filter, dispersion of the pigment in the colored composition is quite important, and use of a colored composition lower in dispersion often results in deterioration in contrast of the color filter produced.
Colored compositions containing a pigment-dispersing agent have been used for production of filter segments, and a sulfonated compound of C.I. Pigment Yellow 138, or a salt thereof produced by neutralizing the compound with an aqueous metal alkali or amine solution, i.e., a sulfonation derivative of C.I. Pigment Yellow 138, has been used as the pigment-dispersing agent in the past (for example, Jpn. Pat. Appln. KOKAI Publication Nos. 9-176511, 2002-179979, and 2003-167112).
However, under the circumstance demanding further improvement in the physical properties, such as dispersion stability, storage stability, and uniformity of the filter segments formed, of the colored compositions for use in production of color filters, the sulfonation derivative of C.I. Pigment Yellow 138 conventionally used is becoming more difficult to satisfy the requirements. Especially in recent years, more liquid crystal displays are used in television monitor application, and there exists a need for higher-concentration color filters containing a greater amount of pigment for production of such panels.